Transmission Control Protocol (TCP) is a lower level connection protocol. TCP is used in a router by higher level routing protocols, such as Border Gateway Protocol (BGP), for setting up connections with peer routers and exchanging route information with them. In a router with an Active Main Board (AMB) and a Standby Main Board (SMB), TCP and other protocols, such as BGP and Label Distribution Protocol (LDP), run on AMB and SMB. AMB and SMB may also be called active processor and standby processor respectively. TCP High Availability (HA) provides support for the high availability of those protocols that use TCP. When AMB fails, SMB may take over the role as a new AMB smoothly if TCP and other protocols have the high availability capability. The completeness of TCP data messages in TCP HA is a critical part for AMB to be well protected by SMB.
The completeness of TCP data messages in TCP HA mainly involves handling for incoming and outgoing TCP data streams. For an incoming TCP data stream, the completeness makes sure that the application in SMB receives the incoming TCP data from the beginning of an application message when it starts to accept the data. From the beginning point of the incoming data stream, the application in SMB may get continuous data that contains whole application messages. For an outgoing TCP data stream, the completeness guarantees that the application in SMB obtains the outgoing TCP data originated from the corresponding application in AMB from the beginning of an application message when it starts to snoop the outgoing TCP data. From that beginning point of the outgoing data stream, the application in SMB may get continuous data that contains whole application messages. When a failure in AMB happens, a procedure called switch over from AMB to SMB is triggered, during which SMB takes over the role as a new AMB, the completeness makes sure that the transmission of every incoming and outgoing TCP data stream is seamlessly switched over from AMB to SMB, that is, the whole application messages flowing continuously are sent to the peer router from every outgoing TCP data stream in the new AMB and these whole application messages are delivered to the application in the new AMB from every incoming TCP data stream. A switch over from AMB to SMB may also be triggered when a “switch over” command is issued by a user.
Conventional systems and methods for the completeness of TCP data messages in TCP High Availability (HA) use explicit application message boundary notifications. For an incoming TCP data stream associated with a socket, an application using this TCP socket in AMB must recognize at which particular message boundary the corresponding application in SMB will begin to receive the duplicate application messages on the corresponding replica socket. The boundary information, corresponding to a sequence number for the last byte of an application message, is forwarded to TCP in AMB, which passes the sequence number to TCP in SMB. TCP in SMB may start to deliver the incoming TCP data to the corresponding application in SMB according to the sequence number. For an outgoing TCP data stream associated with a socket, the application using this TCP socket in AMB identifies at what point each application message boundary is, and the application passes this boundary information to TCP through the socket. TCP in AMB sends the message with this additional information to TCP in SMB, which interprets and strips the additional information and sends the message to the corresponding application in SMB.
The conventional systems and methods may encounter a number of problems. For example, an application using TCP for receiving incoming data notifies TCP, application message boundary information in the condition that the last byte that the application receives from TCP is the boundary of a message. In some situations, it may wait for a long time for the condition to be satisfied. Thus it may take a long time for AMB to become fully protected by SMB. Another shortcoming of the conventional systems and methods is, that applications using TCP for sending data must tell TCP application message boundary information for every piece of data written to TCP. In addition, TCP needs to be enhanced to accept the boundary information from the applications.
Therefore, there is a need of systems and methods for the completeness of TCP data messages in TCP HA that works more efficiently, simplifies the interface and interactions between application and TCP, and minimizes changes in TCP and applications using TCP.